Continuous growth of hydrogenetic ferromanganese crusts since 17 Myr ago on Takuyo-Daigo Seamount,NW Pacific,at water depths of 800–5500 m |
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| Institution: | 1. Center for Marine Core Research Institute, Kochi University, Japan;2. Institute for Industrial Science, University of Tokyo, Japan;3. R & D Center for Marine Resources, JAMSTEC, Japan;4. Metals Exploration Dept., JOGMEC, Japan;5. Division of Chemistry, Tsukuba University, Japan;6. Geological Survey of Japan, National Inst. Advanced Industrial Science and Technology (AIST), Japan;7. Tokyo University of Pharmacy and Life Sciences, Japan;8. Emeritus Professor, University of Tokyo, Japan;1. Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan;2. Geological Sciences, The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, USA;3. Faculty of Science, Kochi University, 2-5-1 Akebono-cho, Kochi 780-8520, Japan;1. Saint-Petersburg State University, St. Petersburg 199034, Russia;2. Institute for Geology and Mineral Resources of the Ocean (VNIIOkeangeologia), St. Petersburg 190121, Russia;3. U.S. Geological Survey, Santa Cruz, CA 95060, USA;4. The Laboratory HERCULES, University of Evora, Évora 7000-809, Portugal;5. Estrutura de Missão para a Extensão da Plataforma Continental, Paçod''Arcos 2770-047, Portugal;6. Universidade de Évora, Instituto de Ciências da Terra, Dep. de Geociências, Évora 7000-671, Portugal;1. Kochi University, B200 Monobe, Nankoku, Kochi 783-8502, Japan;2. Research Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, Central 7, 1-1-1 Higashi, Tsukuba 305-8567, Japan;1. Department of Geology, Graduate School of Integrated Arts and Sciences, Kochi University, Japan;2. Department of Geology, Kochi University, Japan;3. Sumiko Resources Exploration and Development, Co., Japan;4. Center for Advanced Marine Core Research, Kochi University, Japan |
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| Abstract: | Ferromanganese crusts cover all outcrops on Takuyo-Daigo seamount traversed during remotely operated underwater vehicle (ROV) dives, except in places covered by foraminifera sand. Takuyo-Daigo is a Cretaceous seamount located in the northwest Pacific Ocean. Geological and bathymetric mapping provide the framework for this study. Chemical and mineralogical analyses of the hydrogenetic ferromanganese crusts show temporal and spatial variations typical of those found in previous studies. Outcrops from 800 to 5500 m water depths are covered with ferromanganese crusts up to 105 mm thick. Beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths, even through the modern oxygen minimum zone (OMZ), contrary to some earlier models for deposition. Growth rates vary from 2.3 to 3.5 mm/Myr, with Fe or Mn fluxes of 0.07–0.11 g/cm2/Myr since the early-middle Miocene. Co/Mn ratios decrease with water depth while Fe/Mn and other metallic elements increase or show no change, based on the analysis of the uppermost crust surface. This is probably because Co is the most abundant redox-sensitive element derived from seawater that occurs in crusts. |
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